Balloon systems have been used for decades to carry atmospheric sensors, surveillance equipment, and communications gear to various altitudes. Substantial prior art is documented in The Moby Dick Project: Reconnaissance Balloons Over Russia by Curtis Peebles (1991, Smithsonian Books), as well as in a lengthy Air Force bibliography located at http://www.wrs.afrl.af.mil/library/balloon.htm. In general, earlier, systems either used a disposable payload, or a parachute system to return the payload safely to the ground. Older parachute systems were uncontrolled, but sometimes provided tracking signals; payload recovery involved either elaborate airborne snatches or extensive hunting over the landing zone. More recent systems, disclosed in various NASA research reports add guidance and control capabilities to the parachute, providing some flexibility to choose a landing site within a small target range. Inflation and launch has historically required calm weather and numerous personnel.
Certain applications require low-cost, rapid deployment of payload capability over an area of interest, with minimal operations personnel and maximal probability of retrieving the payload. Such a capability demands a system that can be launched on very short notice by as few as one to two people, ascend to the target altitude and location automatically with as little energy expenditure as possible, and return the payload to the point of launch or another designated spot as safely as possible.
In view of the above, the present invention provides a solution to the need cited above. As those skilled in the art recognize, there can be many different implementations of the present invention. For example, an embodiment of the present invention can include may aspects of the invention, including some of the following.
A cylindrical plastic-film balloon envelope design is used to provide an inexpensive buoyant platform. This design is well-known to those skilled in the art as being easy to manufacture in quantity, because it does not require the design specific curved scams of a so-called “natural shape” envelope. A range of envelope sizes can be provided so that a deployable system can fly individual platforms at any altitude as required by the application and weather conditions; for example, five “family” sizes can cover the range from 60,000 feet to 100,000 feet altitude for one specific payload mass range. A novel adjustable end-fitting can be provided so the specific balloon volume for the desired altitude required can be set at launch time. The system operator simply selects the smallest family size that can reach the required altitude, adjusts the end fitting to the precise balloon length needed, and cuts off excess material. While cylindrical envelopes are used in an embodiment to provide inexpensive lift, other shapes can be used in an alternate embodiment to optimize the flight differently. For example, a natural shape envelope could be used to increase envelope performance or efficiency. Additionally, an aerodynamically shaped envelope could be used to provide a tactically launched high altitude airship. In this case the PRV would be powered to provide the airships propulsion system.
A pair of techniques from prior art are used to simplify launch procedures and reduce personnel requirements. Because these balloons are very large, when filled they present significant surface area to any wind present at launch. This can be a substantial safety hazard to launch personnel, and creates a great risk of equipment loss. To reduce the surface area at launch, thereby reducing the risks and allowing the platform to be launched in higher winds, a two-cell design is used. A smaller tow cell is attached to the larger main cell, so that the main cell remains unfilled until the pair has accelerated to a speed close to that of the prevailing winds, thereby minimizing the effective wind load on the large main envelope. In addition, the main balloon cell is packed in a deployment bag which includes an automatic release mechanism. When an appropriate altitude or time after launch is achieved, a control system activates the release mechanism, thereby deploying the main cell. Rather than a large sail area at launch, the packed main cell is a compact bundle that does not catch any wind. This elimination of surface area reduces the potential for damage to the gossamer structure due to high wind loading; it also reduces the number of personnel required by making the “launch train” dramatically shorter, in turn eliminating related hazards to personnel and equipment at launch. The tow cell and the main cell are connected via an intercell tube fitting, so that as the combination rises the buoyant gas expands to fill both envelopes.
For certain flight requirements, management of lifting-gas flow between the tow cell and the main cell may be accomplished via a valve in the intercell tube fitting. This valve is controlled by the platform management computer (see below) via a wireless local communication link that is separate from the main platform communication links described below. Using a wireless link for this local communication avoids the complication of adding flexible wires to the packed main cell, and is a novel approach. During ascent, closing this valve prevents further expansion of the lifting gas into the main cell envelope, which stops the ascent at a particular altitude. Reopening the valve permits the lifting gas to continue expanding into the main cell, thereby resuming the ascent. In an alternate embodiment, the valve may be installed in the tow cell's top fitting, allowing the ascent to be slowed or stopped by venting lifting gas rather than forcing it into the main cell. Depending on altitude, duration, and the amount of free lift required for a particular flight profile, to store the extra lifting gas that may be used in either of these altitude control schemes the tow cell may be enhanced to “super-pressure” capability so that it can accommodate the gas pressure that builds behind the closed valve as the platform rises. While super-pressure balloons themselves are known to those skilled in the art, their simultaneous application as a tow cell and as a gas reservoir in a multicell platform is novel.
A novel apparatus is also used to further simplify launch procedures, reduce personnel requirements, and expand the range of wind conditions in which launch can be accomplished. An adjustable, durable fabric tent is used to enclose the tow cell while it is being filled prior to launch. Weighted along its length and anchored at the filling end, this tent, or launch bag, provides a calm environment in which to fill the tow cell with buoyant gas. The launch bag is designed with an opening at one end that permits attachment of a filling hose to the enclosed tow cell, and an opening at the other end through which the intercell tube fitting mentioned above protrudes so that the main cell and payload may be attached to the tow cell after it has been filled. The launch bag is designed so that its size can be adjusted to match the volume of lifting gas required for a particular launch. Filling of the enclosed tow cell can be easily terminated upon achieving the preset volume, either manually by observation of the achieved size, or automatically by use of a back-pressure shutoff mechanism in the fill nozzle. After the tow cell is filled, the fill nozzle is removed, and the main cell and payload are attached. Since the attachment point for these items is at the center of the tow cell's circular cross-section, they rest on a cradle which is designed both to hold them up and to roll around. Because of the anchor and weight arrangement described above, as well as the rolling cradle on which the payload rests, the entire assembly can adjust with changing winds, providing an optimal positioning for launch without personnel or vehicles having to move around carrying the flight train. Launch is performed by pulling open a single hook-and-pile (Velcro) seam along the top of the launch bag, thus releasing the tow cell into the air. Layout, adjustment, filling, payload attachment, and launch can be performed by as few as two persons in its current embodiment or by a single individual with the addition of package handling straps. While the use of such an apparatus is inspired by the prior art “covered wagon” system (see Peebles 1991 cited above), the present launch bag offers significant improvements on that device. First, the launch bag is constructed entirely of fabric, and sized for the tow cell in the present multicell platform rather than a much larger single-cell platform, so it can be handled easily and stored/transported compactly; the covered wagon was a hard-sided truck trailer sized for a large single envelope. Second, the tent-like structure of the launch bag fills with wind, stabilizing the launch bag, and aiding in optimally orienting the launch system parallel to changing winds with a minimum of human interaction; in contrast, the covered wagon uses a hard sided trailer to completely shelter the balloon from the wind and would require motorized trailer movement for optimal orientation to changing winds. Finally, the launch bag and filling process are integrated such that the size-adjusted bag controls the volume of lifting gas filling the tow cell automatically. Operating personnel simply set the bag for the desired payload/altitude combination and a backpressure shutoff valve in the fill nozzle stops the flow of buoyant gas into the tow cell without further operator intervention. These improvements combine to create a novel launch system that can be used for tactical deployments in high winds.
The payload may be encapsulated in a payload return vehicle (PRV), which is an aircraft designed to be released from the balloon after it can no longer remain in the area of interest, then fly to a predetermined location and land safely. The landing location may either be the same as the launch point, or some other location determined by application requirements. In general, the payload return vehicle is a lightweight airframe capable of autonomously recovering to stable flight after being dropped from the balloon in very thin atmosphere (also known as “pulling out”), navigating to the landing location, and landing automatically. Return flight and landing may optionally be taken over by a pilot via a remote-control mechanism. The PRV may be of any size and configuration appropriate to the payload for a particular application, with the balloon platform size(s) being adjusted accordingly. In an embodiment, the PRV is of a size and weight such that it can be handled by one or two people in order to align with the launch-complexity goals of the novel launch subsystem described above. Depending on the application requirements such as loiter time, return distance, stealth, and others, several degrees of freedom can be exercised in PRV choice. For example, low aspect ratio, high aspect ratio, or hybrid formats may be used. Either gliding or powered variants are possible, and power plants can incorporate any kind of engine including propeller, jet, or rocket. Propulsion may be optimized for low-altitude performance to extend the return range, for high-altitude performance to assist in station-keeping, or both. The PRV may be constructed from any of several different types of material depending on application requirements such as speed, strength, or serviceability. For example, the PRV may be primarily constructed from polymer foam sheets, with wood and fiberglass reinforcements at high-stress points. Depending on application requirements, other materials may be appropriate as well, including composites, metals, films, or fabrics. Payload accommodations may include shock-resistant cases, dedicated attachment points, integrated/active surfaces (such as radar or communication antenna panels, openings, or embedded optical lense's), extension/retraction mechanisms, and/or reserved volumes as appropriate to the application. Payloads may provide communication support, data collection, observation, radar, or any other function that may benefit from operation in near-space.
An example PRV is a faceted lifting-body design derived from Barnaby Wainfan's FacetMobile (http://members.aol.com/slicklynne/facet.htm). This design provides a low-cost, easily repairable platform that performs well in atmospheric densities from sea-level to at least 100,000 feet. Its low-aspect-ratio form factor offers ample allowance for payload integration; relative to the overall size of the aircraft, large internal volumes are available for installing equipment, and very large surfaces are available for integrating flat active devices such as radar or communication antenna panels. The low aspect ratio also supports safer launch and landing behaviors due to the relatively short wingspan.
In an embodiment, the FacetMobile PRV can be primarily constructed from polymer foam sheets, with wood and fiberglass reinforcements at high-stress points. These materials are inexpensive, leading to a low-cost aircraft. They also are relatively simple to work with, supporting a high-tolerance, low-skill manufacturing process and rapid, low-skill field repairs.
In an embodiment, a hard-shell carrying case payload pod can be provided to contain and protect payload electronics. The case is easily removable, and in the event of a hard landing will protect the payload from damage. It can also be carried away from a crash site intact even if the PRV itself is irreparable. Carrying cases of suitable size and strength are readily available on the open market, and are well known to those skilled in the art. Certain modifications are required, however, in order to provide holes for mounting the case to the PRV and for attaching to the balloon-system release mechanism.
In an embodiment, a payload pod access panel can be provided on the PRV bottom facet. This opening provides easy access to the PRV interior for installing and removing the payload pod described above. The PRV speed brake is embedded in the access panel, and so its control connections are modified to be easily detached.
In an embodiment, payload pod mounting brackets can be provided inside the PRV to accommodate the shape and attachment points of the hard-shell carrying case described above, thereby providing a secure installation and simple removal.
In an embodiment, a detachable PRV nosecone can be provided to house all platform avionics separately from the payload pod to maximize payload capacity while providing optimal interchangeability among PRV airframes and control subsystems. In an alternate embodiment, the platform avionics are collocated with the payload inside the aforementioned hard-shell carrying case.
In an embodiment, a removable PRV vertical stabilizer can be provided, into which a payload antenna may or may not be embedded as required by a particular payload. The optional vertical stabilizer can support and provide aerodynamic cover to an antenna if required. A mounting system can be provided on the appropriate facet that makes the combination stab/antenna interchangeable with a non-antenna stab or a filler for no stab at all.
The PRV is integrated with the buoyant platform in two novel respects. First, the control avionics and release actuators for the balloon are carried in the PRV so that disposable elements are reduced and the sophisticated control elements can be recovered along with the payload. Second, ballasting mechanisms and materials are carried in the PRV so that ballast can be discharged from the bottom of the flight train rather than risking damage to the PRV and its payload due to ballast falling from the balloon above; this design has the additional benefit of allowing the PRV to utilize any ballast that remains from balloon operation to increase wing loading, enhancing its ability to overcome higher adverse winds during the return flight.
The combined lift/return platform includes appropriate control componentry, including an autopilot, communication links, and a platform management computer with sensor and driver interfaces for both platform-specific functions and payload control. The autopilot handles automatic navigation, flight stability, and landing of the PRV during return flight. Two bidirectional communications links are provided. A high-speed line-of-sight (LOS) channel supports manual piloting by an operator on the ground if that is appropriate in a particular application. A low-speed beyond-line-of-sight (BLOS) channel permits a ground operator to monitor platform status and change flight plan parameters as necessary. In an embodiment the LOS channel is a license-free radio operating in an ISM band, while the BLOS channel is an Iridium satellite modem. Alternate embodiments may use other channels as appropriate for a specific application. The platform management computer controls main balloon deployment, ballast release, super-pressure balloon gas valving, and PRV release. It can also enable and disable payload power, and depending on the specific application it may sense and report on payload health and status or be used for payload telemetry and control. In an embodiment the autopilot and platform management computer are implemented as separate units with appropriate interconnects; in an alternate embodiment these functional elements may be integrated into a single unit.
The autopilot and platform management computer use the communication links to interact with system operators via a compact ground station. This ground station provides an operator with appropriate status information and command capabilities in accordance with principles well-known to those skilled in the art. A novel mission planning capability is also provided, wherein the buoyant platform's ascent and loiter, and the PRV's return flight, are modeled in the context of prevailing and forecast atmospheric conditions (primarily wind speed and direction) and aerodynamic characteristics of the specific PRV design. System operators use this information to plan launch location and timing, PRV release location and timing, and flight plan changes if necessary. The ground station is capable of managing multiple simultaneous ascent, loiter, and return flights in support of continuously delivering fresh platforms to an area of interest and retrieving spent payloads.